To provide a sheet postprocessing device capable of preventing bad sheet stitching and poor sheet feed by controlling each of sheet conveyance and sheet alignment depending on the thickness and strength of a sheet.

A sheet postprocessing device 1 includes: a staple tray 43; a pair of shift rollers 31 which carry sheets S into a staple tray 43; a reference fence 47; a hitting roller 33; a contact/separation driving unit 106 which brings the hitting roller 33 into contact with/separation from the sheets S; a carrying roller 45 which is provided on the side of the reference fence 47 with respect to the hitting roller 33 and which carries the sheets S to the side of the reference fence 47 by abutting on the sheets S stacked in the staple tray 43; and a control circuit 6 which receives sheet information on the sheets S, set by an image forming apparatus 81. The control circuit 6 changes control of each of the contact/separation driving unit 106 and the carrying roller 45 on the basis of the sheet information.